Gas turbine engines as utilized in the aerospace industry must undergo stringent testing prior to certification. Such testing includes various failure modes of the engine, wherein one or more components of the engine are induced to failure, and the engine reaction to such failure must meet certain standards. For example, one such testing for certification contemplates the loss or failure of a compressor or turbine blade within the engine, and the subsequent ingestion of the broken part through the engine. Dependent upon a particular test the engine must maintain certain minimum performance, and/or comply with controlled failure specifications. Such testing and the results therefrom are most valuable and accurate if they reasonably and reliably occur under conditions of the gas turbine engine as it would be used in service.
A typical prior arrangement for deliberately inducing a failure of a compressor or turbine blade within a gas turbine engine is illustrated in FIG. 1. Here an airfoil 10 has deliberate undercuts 12, 14 machined in a narrow, neck section 16 between the airfoil platform 18 and its root 20. This test blade is inserted in a turbine or compressor wheel of a gas turbine engine which is then run up through speed and power. If failure does not occur, the engine must be disassembled, the undercuts 12, 14 increased in size, and the process repeated gradually until release of the blade occurs to permit the test to proceed. Of course, if the test blade fails prior to reaching the required speed and power of the engine, not only must the test be repeated, but also the entire engine or significant portions thereof must be rebuilt.
These methods for testing a gas turbine engine can be quite time consuming and high in cost. Further, due to the near constant strength of the blade material over the operational temperatures it experiences in the engine, the test blade tends to fail as a function of speed rather than of time. Thus, it may be difficult to determine whether or not the remainder of the engine has reached its normal operating condition (i.e., whether all components of the engines have reached their steady state operating temperature) at the time of the blade release.